Soy rust in Louisiana kudzu

As the Mid-South leaves a wet spring and heads into summer with an abundance of late-planted soybeans, what’s going on with Asian soybean rust?

One key man to ask is Clayton Hollier, LSU AgCenter plant pathologist. Hollier, who works out of a Baton Rouge office, has been monitoring soybean rust for years. He spoke to Delta Farm Press in late May. Among his comments:

Can you provide our readers with a run-down of what you’ve found this year?

“We’ve found (Asian soybean) rust throughout the winter. This is the first time there hasn’t been a break in the disease cycle through the winter at the site just outside New Iberia. Iberia Parish is in the south-central part of the state.

“At that site, the rust has exploded. There are yellowing kudzu leaves due to rust working them over. Symptoms aren’t that extreme on every leaf, but on other leaves rust is also readily apparent.

“My research associate is still checking that kudzu even though we now have soybeans growing in our sentinel plots. However, the soybeans aren’t far enough along for us to have found any rust. The oldest sentinel beans are probably around R-1. The youngest beans in the plots are only a few inches high because of late plantings due to wet weather.”

On weather conditions favorable to soybean rust…

“Afternoon and evening temperatures have been relatively mild lately. Moisture is also plentiful — rains are coming almost every day. Sometimes we’ll have just a shower and sometimes a couple of inches worth.

“Rains have been variable around the state. The extreme western half of Louisiana — next to Texas — hasn’t had quite the rain that has fallen in other parts of the state.

“Regardless, it’s very wet here. I went out to my corn plots this morning and needed rubber boots. Farther north, towards northeast Louisiana, there’s been even more rain. Some of our soybeans have been drowned out, although none of our sentinel plots, thank goodness. In fact, those plots are growing quite well.

“The New Iberia kudzu location is very interesting. We’re monitoring it and trying to find any spread of rust from there. So far, there’s been no spread. But, right there, it’s very heavy.”

It calls for speculation, but why there?

“We’ve suspected for two or three years that rust has overwintered there. However, normally (infected) sites have gotten a frost or low temperatures late in the year that knocked the rust back and we couldn’t find it afterwards. Yet, when spring rolls around and there’s plant growth, we’d very quickly find new pustules beginning to form.

“We’d think, ‘Well, wait a second. How did this happen?’ Through strictly circumstantial evidence, we figured the rust had to be surviving in that location somehow.

“This year, though, we’ve never lost sight of the rust.

“Let me explain the site. It’s in back of several apartment buildings with large trees, a big drainage ditch behind the trees and kudzu growing all over the ditch banks and into the trees. Some of the kudzu isn’t more than 10 or 12 feet from the back of the buildings.

“I suspect because of the tree cover, wind blockage and the warmth that’s likely radiating from the apartments the rust has been able to survive easier.”

“Sentinel plot funding actually comes late in the year. That means we’re currently using 2008 money, which we began using at the end of last year. We’ve been able to stretch those funds so we can get through the rest of this calendar year.

“Now, there are no frills. A salary, benefits and travel is being paid out of it. We won’t be able to do some of the things done to help cooperators previously. But we’ll get through the year.

“Next year is a huge concern, though. I’m not sure what will happen with rust-monitoring funding. We need that funding to keep the (surveillance) program going.”